Along with development and exploitation of renewable energy like solar cells and wind turbines, the sources of power become diversified. In order to acquire higher power conversion efficiencies, it is not appropriate to connect too many solar cell panels in series. Under the same rated power, solar cell panels are usually installed as a parallel-connected module having a low voltage and a large current, i.e., a low voltage source. In order to reduce the loss caused by the armature current, a wind turbine usually adopts a winding design having a high voltage and a small current, i.e., a high voltage source. In consideration of these differences, a dual input DC—DC power converter is required for directly integrating DC power sources of different electrical specifications from the solar cell panels and the wind turbine.
Although many methods for paralleling DC sources have been developed, there are limits and drawbacks, especially for these with obvious voltage amplitudes differences. In a conventional method, after two DC voltage sources are respectively processed by two individual DC—DC power converters, stable and identical output voltages are obtained. These two voltage sources are then connected in parallel to a DC bus to provide power for a load. However, because two DC—DC power converters are required, the whole circuit architecture of the power conversion system will be complicated, the efficiency will be inferior, and the cost will be high. In another conventional method, two voltage sources are connected in series to form an input power source, which is connected to a DC—DC power converter to achieve the required electrical specification of the load. However, a switching bypass is required at the series input end of the voltage source so that another power source can still provide electric energy when one power source fails. Therefore, the structure can not be effectively simplified, and the operation is inconvenient.
Besides, in yet another conventional method, two DC voltage sources are connected in parallel to form an input power source, which is connected to a DC—DC power converter to achieve the required electrical specification of the load. Because of different voltage levels of the two parallel-connected voltage sources, it is necessary to adopt a time-sharing control method. However, at a certain time, only a voltage source can be connected to the power converter to provide power for the load end. That is, the two voltage sources can not simultaneously transfer power to the load end.
Accordingly, the present invention aims to provide a dual input DC—DC power converter suitable for a high and a low voltage sources to effectively solve the problems in the prior art.